Abstract
The structural build-up of cementitious paste with nano-Fe3O4 under time-varying magnetic fields was experimentally investigated using small amplitude oscillatory shear (SAOS) technique. Several modes of magnetic fields, such as constant, sudden-changed and linearly-changed, were applied to the cementitious paste. Results showed that the structural build-up of the cementitious paste depended on the magnetizing time and magnetic field strength. Applying constant magnetic fields improved the liquid-like behavior during first minutes and afterwards the solid-like property was enhanced. Both the sudden-increased and sudden-decreased magnetic fields resulted in a sharp decrease in storage modulus. The linearly increasing magnetic field resulted in a slight increase in storage modulus but higher liquid-like behavior. When the magnetic field was linearly decreased from 0.5 T to approx. 0.25 T, the structural build-up was enhanced significantly, and with the continuously decreasing magnetic field from approx. 0.25 T to 0 T, a decrease in storage modulus was observed.
Highlights
The cement production of the European Union in 2016 increased to 169.1 million tons, ranking third behind China and India, according to the activity report (2017) published by the European Cement Association (CEMBUREAU)
The experimental results of pure Portland cement paste with w/c of 0.4 under external magnetic field of 0 T was presented as a reference (Ref)
The time when the phase angle starts to stabilize or the storage modulus starts to increase steadily is defined as percolation time, which can be used to describe the time for colloidal particles to reach their equilibrium positions [29]
Summary
The cement production of the European Union in 2016 increased to 169.1 million tons, ranking third behind China and India, according to the activity report (2017) published by the European Cement Association (CEMBUREAU). By actively controlling the rheology and stiffness, the structuration rate of fresh concrete could be adjusted artificially according to the requirements at different operation processes for the same concrete mixture, which could make the pumping and casting processes smarter and more reliable. After water is in contact with cement particles, the C3A and C4AF start to hydrate with gypsum to form ettringite During these hydration processes, the dissolution concentrations of iron increase, resulting in cement paste exhibiting a slight magnetic behavior [21]. Under extremely low shear strain, the rheological properties such as storage modulus and static yield stress of pure Portland cement paste only showed a limited change under external magnetic fields. In order to achieve the goal of actively triggering the rheology and stiffness of fresh concrete, it is necessary to comprehensively understand the magnetorheological behavior of cementitious paste under the application of magnetic fields. This study provides some preliminary concepts that will contribute to actively controlling the rheology and stiffness of fresh concrete
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